The present invention relates to a display suitable for monitoring communication conditions of each channel in multi-channel communications using a plurality of sub-carriers such as OFDM (Orthogonal Frequency Division Multiplex) systems.
OFDM systems have been widely employed in multi-channel communication standards using a plurality of sub-carriers, such as wireless LAN (Local Area Network) systems, Wi-Fi, WiMax, etc. For more efficient communication in such communication systems, the number of sub-carriers and modulation types to be used for each channel change from time to time in response to the amount of data to be sent or received and the communication environment. As for modulation types to be used, the data transmission rate is prioritized using a modulation type such as 16 Quadrature Amplitude Modulation (16QAM) or the like having a high data transmission rate (i.e., bit rate) per unit time for each channel in case of good transmission and receiving environment. On the other hand, reliable data transfer is prioritized using a modulation type of low bit rate such as BPSK (Bi-Phase Shift Keying) or the like in case of poor transmission and receiving environment.
In order to ensure stable communication quality, it would be useful to continuously monitor dynamic changes of wireless signals over time. A known measurement equipment for measuring such signal (i.e., signal to be measured), particularly in frequency domain is a spectrum analyzer. Many attempts have been made to measure such signals using a spectrum analyzer.
For example, U.S. Pat. No. 6,219,340 discloses in its specification an invention to graphically display the condition of a signal to be measured for easily understanding the condition of the signal to be measured. In this US patent, a bar corresponding to each channel of a Code Division Multiple Access (CDMA) signal, which is a communication system utilized in cellular phone systems, is displayed in such a manner that width of the bar indicates which code layer is in active condition. However, the display lacks the time axis, thereby failing to clearly indicate how each channel changes over time.
In wireless LAN systems, or the like, the most efficient data transmission is achieved by timely changing the number of sub-carriers to be used for each channel and the modulation types depending on communication environment that changes from time to time. Unfortunately, however, it was difficult in the prior art to easily understand how changes were made relative to time.